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05-31-2009, 06:46 AM   #1
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1/250 HSS vs 1/180 X-sync

I'd be happy if someone with an HSS-capable flash will check the flash range for each of the following settings:

- 1/180 X-sync, f/4.0
- 1/250 HSS, f/4.0
- 1/250 HSS, f/3.5
- 1/250 X-sync (any Z-1/PZ-1 owner in the house?), f/3.5

Thanks!
Prog.

05-31-2009, 11:29 AM   #2
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QuoteOriginally posted by Prognathous Quote
I'd be happy if someone with an HSS-capable flash will check the flash range for each of the following settings:
- 1/180 X-sync, f/4.0
- 1/250 HSS, f/4.0
- 1/250 HSS, f/3.5
- 1/250 X-sync (any Z-1/PZ-1 owner in the house?), f/3.5
Not sure I have time to actually test, but in the manual Metz lists the maximum HSS GN of the 48 AF-1 (at narrowest zoom) as 21, and 26 for the 58 AF-1. In both cases, that a little less than 45% of the distance (and about one fifth of the raw power).

I'm not sure what shutter speed that's measured at given how HSS works, the maximum will go down as the shutter speed gets faster, and may even be decreased from the max at 1/250th.

So it's definitely fair to say that HSS is no substitute for a faster flash sync. On the other hand, 1/180th to 1/250th is just half a stop, so while I'm sure it'd help people it seems like only a marginal improvement. Improving high-ISO noise performance by half a stop would serve the same purpose and have a much wider benefit.
05-31-2009, 01:43 PM   #3
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I have to agree with mattdm. I remember when a fast x sync speed was 1/60 of a sec, so 1/180 is fast. Beside, what freezes the movement is the flash duration, not the sync speed.
05-31-2009, 02:15 PM   #4
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QuoteOriginally posted by flyer Quote
I have to agree with mattdm. I remember when a fast x sync speed was 1/60 of a sec, so 1/180 is fast. Beside, what freezes the movement is the flash duration, not the sync speed.
Fast flash sync is in most situations not meant to freeze motion, but to keep the background light level low, in order to use a wider aperture for reduced DOF: portraits in daylight, where you would use fill-flash and similar situations.

Ben

05-31-2009, 04:26 PM   #5
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QuoteOriginally posted by Ben_Edict Quote
Fast flash sync is in most situations not meant to freeze motion, but to keep the background light level low, in order to use a wider aperture for reduced DOF: portraits in daylight, where you would use fill-flash and similar situations.

Ben
Keeping the background light levels low while using flash is a style, not a technical reason for high sync speeds. It's a stylistic choice to darken the background. It's just as valid to balance daylight with flash without darkening anything.

You typically only see very high sync speed with cameras that either have electronic shutters, or leaf shutters.

If you work it out, 1/250 sync speed is 1/2 a stop faster than 1/180, so you aren't getting that much benefit.
06-01-2009, 04:34 AM   #6
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QuoteOriginally posted by alohadave Quote
Keeping the background light levels low while using flash is a style, not a technical reason for high sync speeds. It's a stylistic choice to darken the background. It's just as valid to balance daylight with flash without darkening anything.
My reply was probably too short - but what you wrote is exactly what I aimed to say...
Ben
06-01-2009, 06:53 AM   #7
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Thanks for the replies guys. If anyone can post the actual distance numbers reported by such a flash (e.g. 540FGZ), under these parameters, it would be great.

Prog.
06-01-2009, 12:25 PM   #8
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Food for thought

QuoteOriginally posted by alohadave Quote
If you work it out, 1/250 sync speed is 1/2 a stop faster than 1/180, so you aren't getting that much benefit.
Before you go too far down this line, you need to consider that there are 3 parts to a shutter open time.

You have the leading edge transit time, the full frame exposure time (zero above sync speed) and the trailing edge transit time, (same duration as the leading edge transit time)

While I have not tested yet, (something I plan to do ultimately) I am a firm believer that shots taken with my AF540FGZ on my *istD are not as sharp as those taken with my AF500FTZ, when I use my SMC 300 F4 and TTL mode.

both flashes are ~GN=50 (ISO100) BUT the AF500FTZ was made to work with the shutter on the PZ-1 which had 1/250 sync speed. I am very sure that the duration of the maximum power burst was much shorter than the AF540FGZ which is used on the Pentax DSLRs. Note also that there are some postings that report the AF540FGZ has some full power illumination uniformity problems above 1/150 on the K10D, and the inferred meaning was that the duration was longer than the full open time.

At one time I asked pentax about this, and I think they responded that the full frame open time on the PZ-1 was about 1 mS. I got no response regarding the K10D shutter

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